1. Field of the Invention
The present invention relates to a pile driver, in particular, relates to a wire rope press-in pile driver to operate an operation unit such as an auger drive which rises and falls along a leader with a press-in winch via a press-in rope.
2. Description of the Related Art
A wire rope press-in pile driver performs piling operation by repeating to press-in a pile by compulsorily lowering an operation unit which rises and falls along a leader via a press-in rope wound at a press-in winch and to elevate the operation unit via an elevation rope wound at an elevation winch (i.e., a winding winch) after the piling is completed. In order to repeat the lowering operation and the elevating operation of the operation unit, the press-in winch is to be in a winding state of the press-in rope and the elevation winch is to be in an unwinding state of the elevation rope when the operation unit is lowered. Then, when the operation unit is elevated, the elevation winch is to be in a winding state of the elevation rope and the press-in winch is to be in an unwinding state of the press-in rope.
As such a wire rope press-in pile driver, it is known to configure to draw a wire rope from a drum while applying appropriate tension to the wire rope by adopting a hydraulic circuit configuration in which a press-in winch is automatically to be in a free-fall mode in accordance with winding operation of an elevation winch when winding an elevation rope (for example, see Japanese Patent Application Publication (JP-B) No. 2-9126) and a hydraulic circuit configuration in which a clutch arranged between a drum shaft and a drum of a winch is to be in a semi-engaging state (for example, see Japanese Utility-model Application Laid-Open (JP-U) No. 6-65387).